Treatment of aqueous solutions of acetic acid



Oct. l0, 1939. c. 1 L COUTOR 2,175,879

TREATMENT OF AQUEOUS SOLUTIONS 0F ACETIC ACID Original Filed July 22, 1935 2 Sheets-Sheet 1 lNvi-:NjroR [liar/fs ./alz [0144.5 (naief BY M K lu ,LA ATORNEYS oct. 1o, 1939. C, J. L, COUTOR 2,175,879

TREATMENT OF AQUEOUS SOLUTIONS OF ACETIC ACID Original Filed July 22, 1935 2 Sheets-Sheet 2 62 5l COLUMN ATTORNEYS Patented Oct. 10,I 1939 UNITED STATES PATENT OFFICE TREATMENT OFAQUEOUS SOLUTIONS OF ACETICACID Charles Jean Louis Coutor, Premery, France, as-

signor to Socit Anonyme Etablissements Lambiotte Frres, Premery (Nievre Department),

France 4 Claims.

This invention relates to a process for concentrating aqueous solutions of acetic acid.

Several `methods have been already proposed for concentrating acetic acid in aqueous Csolutions. One of these methods, which has already been described in year 1884 by Goeringconsists in extracting the acetic acid in a liquid phase by means of solvents having a low boiling temperature such as ethyl acetate, ethyl oxide, amylalcohol and the like, the said solvents beingthen separated from the acid by any usual distillation process. The said extracting method which a priori seems to be simple and economical, is however fromr the calorific point of view not so economical as it seems to be, since experience shows that it leads, in order not to necessitate a -too costly extraction material, to the use of quantities of solvent which are equal to several times the volume of the solution to be exha'usted, and the subsequent evaporation and dephlegmation of which require a considerable consumption of heat.

Other methods consist in treating the water and acid mixture in the vapor phase in a column by means of a suitable third body acting as a solvent for the acid. Among such methods it will be well to mention more particularly the method of concentration 'by azeotropic distillation, in which the third body plays the part of a Water carrier and which process requires the total vaporization of the diluted solution and of the carrier.

Now it has been found that it is possible, according to the present invention, to realize a considerable economy of steam by combining in a judicious manner the method of extraction of acetic acid inthe liquid phase by means of a solvent with a method of treatment in the vapor phase.

For this purpose, the invention essentially consists in distilling one part of the Asolution to be concentrated in the presence of a water-carrier or entraining liquid, subjecting the other part to an extracting treatment in a liquid state by means of a solvent for the acetic acid, and evapnorating the extracting solvent at least partially by the heat evolved, in the condensation of the product of the distillation. An extracting solvent is employed which has a boiling point low enough to be vaporized by the heat evolved in the condensate of the distillation, and also is one which forms an azeotrope with. water.

When operating at atmospheric pressure the solvents used for extracting the acetic acid in a liquid phasev are preferably bodies having a low (Cl. 21m- 42) boiling point vsuch as methyl propionate, ethyl acetate, isopropyl oxide, p ropyl loxide or mixtures of such bodies. When-the'vaporization of the extracting solvent is eected at a pressure which is lower than the pressure for the treatment in the vapor phase, solvents having higher boiling points may be used. 'I

The extraction of the acid by the solvent malr be effected in a counter-current device of any type, either static or dynamic.

The process according to the invention may be carried out with the distillation in an azeotropical way of part of the solution to be concentrated; the bodies which may be used as Water carriers are more particularly butyl acetate, mesityl oxide, light wood oils, butyl alcohol, amyl alcohols, ethyl butyrate or mixture of such bodies, or other bodies capable of forming with water an eutectic,

the condensation temperature of which at the pressure at which the treatment iselected is high enough for producing the vaporization of the solvent used for the extraction of the acid in the liquid phase.

The process may be applied also-with a de hydration of the acid in the vapor phase effected inil the presence of a heavy solvent of the acid, more particularly such asheavy wood oils, the vapors which form at the top of the dehydration column, and which are in this case almost exclusively water, are used as before for. vaporizing the light solvent which has beenwused for the extraction in the liquid lphaseprrhilethe heavy oils loaded with acid are submitted to a distillation so that the acid is separated from the said oils.

In both cases the fractions of the solution of acid to be concentrated, which'are intended respectively to be submitted toA distillation and to be treatedby a solvent in the liquid phase, are advantageously so determined that the heat which can be recovered in the` treatment of the rst fraction corresponds substantially to the heat required for the treatment of thelsecond fraction.

Several devices for carrying out the'process according to the present invention are shown diagrammatically and by way of non-restrictive examples in the appended drawings.

In these drawings,

Figure l shows a-'device adapted for the concentration of an aqueous solution of acetic acid which is not loaded with .impurities and with azeotropical distillation.

Figure 2 shows -a device adapted for the con-v centration of an aqueous solution of acetic acid which is not loaded with impurities and with distillation in the presence of a'heavy solvent.

In the example oi Figure 1, I is the supplying vessel containing the solution to be treated. A part of this solution is led by a line 2 with a cock 3 to a heater 4 of the type in which all of the volatile part I the liquid admitted is integrally vaporized in a continuous manner, from which heater the vapors of the acid are led. through a line into a dehydration column 8 lled with butyl acetate. The mixture of steam and butyl acetate escapes approximately i'ree from acid at the top of the column i through a pipe 1, while the condensed acid and water flow out at the lower part of the said column into a column 8 heated at its bottom by a heater 3. 4At I0 concentrated acid ilows out.

'I'he other part ot the diluted acetic acid contained in the supplying vessel I is led through a line Il with a cock I2 into an extraction device I3 of the counter-current type, for instance a turbine apparatus. On the other hand this device also `receives a solvent 'for the' acetic acid such as ethyl acetate, which is brought by a line Il and comes from a decanter I5. 'Ihe water flows out approximately free from acid through a pipe I 6 which leads it to a small column I1 in which it is freed from the dissolved ethyl acetate, the latter being returned through a line Il to a condenser I9, while the water is dischargedv at 2li. The ethyl acetate loaded with acid is led through a line 2l into the bottom of a column 22 provided with a heater 23 which receives through the pipe 1 thevapors escaping at the top of the distillation column 6 and which acts as a condenser for the latter.

At the top of the column 22 a mixture of va-. pors of ethyl acetate and steam escapes which are led through a pipe 24-into the condenser I9. The heterogeneous condensate which is produced in this condenser ilows out intothe decanter I5where it' is decanted and from which the ethyl acetate is returned to the extraction device I3, while the water is led through a pipe 25 to the small column I1 which already receives the exhausted waters coming from the extraction device I3.

The bottom of the column 22 is provided with a heater 23 which vaporizes without cost a part of the v-solvent saturated with acid coming through the pipe 2l from the extraction device I3, the heat for this heater being supplied by the vapors of the column l arriving through the pipe 1; The liquid whichhas not been vaporized in the heater 23 ilows out into the heater 21 through the pipe 26; a new part oi theA liquid is vaporized by the vapors of the eutectic in excess which escapes from the heater 23. 'Ihe non-'vaporized mixture of solvent. wate and acid ilows out ot the heater 21 through the pipe 2l into the column 20 which is heated at its bottom by means or a coil 30 and which exhausts the ethyl acetate and the water from the acid. The vapors of .ethyl acetate and water are returned through a pipe 3l into the bottom ot the column 22, while the concentrated acid is discharged at 32. The column 22 receives from the decanter Il through a pipe 33 a reuxed l part of ethyl acetate which is so controlled as to insure a very low acid titration for the solvent.

which is recovered. A

'Ihe binary mixture or'butyl 'acetate and water which cornes from the iaaeotropical dehydration column 6 and ilows through the heaters 23 and 21 is condensed in these heaters and then in a security cooler 3|. The condensate is led through a pipe 35 into adecanter 38 by means of which the butyl acetate is returned into the column 6, while the neutral water is led through a pipe 31 into ya. small column 28 which exhausts the dissolved butyl acetate therefrom and returns this product as vapor through a pipe 39 to the top of the column 6. The exhausted water is discharged at 40.

In the arrangement according to Figure 2, l is the supplying vessel containing the solution to be treated, for instance a non-tarry aqueous solution of acetic acid. A portion of this solution is conducted through a line 2 provided with a cock 3 into an evaporator l in which it is entirely vaporized, and the vapors are introduced through a pipe 5 into the bottom of a column 6' the upper part of which is illed with wood oils having a boiling point higher than 230 C. The vapor ofwater which escapes at the top of the column 6' with some oil carried with itis conducted through a pipe 1' for use for the vaporization of the solvent which has extracted the acidin the liquid phase, as will be explained hereinafter. The heavy oils which are loaded with acid dow into a dehydration column 8' and pass from the latter into a separation heater i! which permits the complete distillation ofthe dissolved acid. The heavy oils from which the` acid has been exhausted, are taken again by a pump 1I) and forced into the upper part of the column 6' for pursuing the extraction cycle. The acid vapors escaping from the top of the column 69 are led into a column 1I where they are separated fromthe heavy products, and the acid which has been condensed in a condenser 12 is collected in a vessel 13, part of this acid being reiluxed into the column 1I through a pipe 14 provided with a control valve 15. In order to facilitate the separation ofthe acid from the tar, the heater 69, the column 1I, the condenser 12 as well as the collecting vessel 13 are advantageously maintained under a suitable vacuum by means of a vacuum pump 16.

The other portion oi. the solution contained in the vessel I' may be directed through a pipe II' provided with a cock l2 into an extraction imately free from acid through a line I6 and is led to a pre-heater 60 (heated in a manner to be described later) from which it is discharged into a small column I1 in which it is freed from the dissolved solvent; the latter is returned through a line I3' to a condenser I9 while the water is discharged at 2li. On the other hand, the solvent, which is saturated with acetic acid, is discharged in a continuous manner from the exhaustion column I3' through a pipe 2| and is conducted into a vaporization device 23 comprlsing a series of horizontal tubes divided into compartments 23a, 23'b 237, through which the vapors of the water coming from the distillation column i through the pipe 1' pass.

The vapors of the solvent and water in azeotropic mixture, and some of the acetic acid produced in the vaporizer 23 are conducted through a pipe 6I to the bottom or a column 22 at the top of which a mixture of vapors of solvent and water escapes in an azeotropic mixture, which is conducted through 'a pipe 24' into the condenser IS'. The heterogeneous condensate produced in this` latter ilows into a decanter Il where it is decanted and from which the solvent is returned through the pipe Il' to the exhaustion column I3. The Water flowing out of the decanter I5' through the pipe 25 is led into the pipe I6 where it is added to the exhausted waters flowing out of the counter-current column I3', going to the heater 60.

At the bottom of the column 22 a ternary mixture of solvent, acetic acid and water flows out and is directed through a pipe 3|' into a column 29 which also receives through a pipe 62 the non-vaporized liquid which iiows out through e the overiiow of the last compartment 231 of the Il This application is a vaporizer 23'. The said column 29 exhausts from the acid the solvent vand water and the vapors of these bodies are returned through a pipe 28 to the bottom of the column 22', while the concentrated acetic acid is drawn oi at 32. Columns 22 and 29' function in eiect as a single column. The water vapor loaded with heavy oils which comes from the dehydration column E' and iiows through the vaporizer 23' is partially condensed in this latter. The condensate is led through a 'pipe 35' into a decanter 36' where the few heavy oils capable of bbeing decanted are returned to the top of the column 6 while the water which is discharged at 31' is conducted to the sewage. The vapor which has not been condensed in the vaporizer 23 is led by a pipe 63. through the heater GII for the waters which are saturated with solvent and then into a condenser 3l'. 'I'he liquid which has been condensed in both these devices is led through pipes 35" and 35" into the dectanter 36.

division of application tially corresponds to Serial Number 32)5'1/2L'1ed/,Iu1y 22, 1935, now the Charles Patent/No. 2,079,789in the le of which the present claimed subject matter was disclosed and fin which applicant through inadvertence andmistake led as a joint inventor.

I claim:

1. A process for concentrating an aqueous solution of acetic acid which comprises distilling one portion of the acid solution azeotropically with an entraining liquid to dehydrate said solution,. subjecting another portion of the acid solution to an extraction treatment in the liquid phase with a solvent for acetic acid to remove the acid from said solution, and evaporating the extraction solvent from said extracted acid at least partially by the heat evolved in thevcondensation of the vapor of the azeotropic distillation, said extraction solvent having a boiling point low enough so that it can be vaporized by said heat and also being one which forms an azeotropicmixture with water.

2. A process according to claim 1 in which the entraining liquid comprises butyl acetate.

3. A process according to claim 1 in which the entraining liquid comprises butyl acetate and the extraction solvent comprises ethyl acetate.

4. A process according to claim 1 in which the several portions of the acid solution subjected respectively `to the two treatments are so proportionedthat the heat recovered in the treatment f the first mentioned portion substanthe heat required for the vaporization of the solvent which is used in the treatment of the second mentioned portion.

CHARLES JEAN LOUIS COUTOIt.v 

